In personal computer, the computer mice are popular pointing means for input data and cursor control. A conventional mechanical mouse generally employs a rolling ball and at least two encoder wheels for x- and y-axis. The encoder wheels are driven by the roll ball when a user moves the mouse along a flat surface such as a mouse pad. The encoder wheels will intermittently block a light propagation in the mouse and associated electronic signal is generated to control cursor movement on a computer display. However, the performance of the mechanical mouse is degraded after a long time use due to ball abrasion and dust inleakage. Moreover, the mechanical mouse uses a bulky and heavy steel ball, which is also inconvenient for user.
To overcome those drawbacks, an optical mouse is provided and has a light transmitter such as light emitting diode (LED), light receiver such as a photo diode and associated components. The prior art optical mouse should be operated on a patterned surface for modulating a light emitted from the light transmitter. The modulated light is received by the light receiver to identify mouse movement and control cursor motion.
However, the above-mentioned optical mouse required specialized mouse pad for normal operation, the applicability thereof is limited. As the advancement of complementary metal oxide semiconductor (CMOS) image sensor technologies and digital signal processing, the optical mouse can use CMOS sensor array to overcome above problem. The optical mouse may be operated at an non-transparent flat surface and the detected signals of the CMOS sensor array are analyzed to identify mouse movement and control cursor motion.
FIG. 1 shows a section view of partial components in a conventional optical mouse. The conventional optical mouse comprises a light transmitter 10 such as LED for emitting a light beam, a light emitting prism 12 and a light receiver 20 such as CMOS sensor array 20. As shown in this figure, the light emitting prism 12 has a special shape rendering the light beam impinging a work surface 100 with small incident angle. Therefore, a relatively large portion of reflected light from the work surface 100 can be detected by the light receiver 20. Even though the light beam is scattered by an uneven work surface 100, a larger portion of scattered light can be detected by the light receiver 20. The electrical signal associated with the received light is analyzed by a DSP element (not shown) in the mouse to identify mouse movement.
However, in the optical mouse shown in FIG. 2, the light emitting prism 12 with special shape is required such that the light beam has small incident angle as impinging the work surface 100 after experiencing two reflections by light emitting prism 12. The light emitting prism 12 requires considerable effort and cost to manufacture and assemble. Moreover, the multiple reflection by the light emitting prism 12 also cause attenuation in intensity of light beam.